Polycellular tubular grid structures and method of manufacture



Dec. 7, 1965 D. E. DAVENPCDRT 3,222,144

POLYCELLULAR TUBULAR GRID STRUCTURES AND METHOD OF MANUFACTURE Filed Feb. 25, 1963 4 If INVENTOR.

DONALD E. DAVENPORT ATTORNEY United States Patent 3,222,144 POLYCELLULAR TUBULAR GRID STRUCTURES AND METHOD OF MANUFAUTURE Donald E. Davenport, Palo Alto, Calif., assignor, by

mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Filed Feb. 25, 1963, Ser. No. 260,929 22 Claims. (Ci. 29191) The present invention relates, in general, to the production of tubular grid or honeycomb structures and, more-particularly, to the use of high explosives for forming and bonding metallic honeycomb or polycellular tubular grid structures and to the products obtained thereby.

Honeycomb structures suitable for various utilitarian purposes are generally manufactured by methods which involve the bonding of corrugated sheeting, polygonal cross-section tube bundles or the like utilizing adhesive bonding agents or, for high temperature purposes, utilizing brazing, soldering, sintering, and similar methods. The methods employed are generally quite complicated and there are various stringent limitations on the properties, structural configurations, and composition of the components which can be utilized, especially, since the cost of manufacture may be prohibitive for most purposes.

Now it has been discovered that a variety of devices embodying honeycomb or other multicellular tubular grid structures can be produced by a method wherein a high explosive material is detonated in contiguity with an appropriate assembly of structural components under proper conditions so as to shape and fuse the components into an integral unit. In a basic sense, in accordance with the invention, a plurality of relatively slender elongated elements having a surface cladding of metal encompassing a deformable core material are disposed within a tubular shell. A jacketing layer of an appropriate explosive is then disposed in encompassing relation along at least a portion of the length of said shell with explosive force modifying material disposed as required to provide desirable effects, together with gas sealing means if necessary to exclude the gases produced upon detonation of the explosive from selected areas of the assembly of the shell and included elements. In the majority of instances interstitial areas within the shell and between said elongated elements should be evacuated to moderate residual gas pressure levels to eliminate gas which may interfere with proper shaping and fusing of the components. The high explosive is then ignited in such a manner as to produce an annular detonation front with an associated compressional shock wave which progressively propagates along at least a portion of the length of said assembly causing an inward deformation of said shell, deformation of the included elements and the bonding or fusing of adjacent cladding and exterior shell surfaces. Thenceforth, utilizing a variety of subsequent operations and finishing treatments as described more fully hereinafter, a variety of utilitarian multicellular tubular grid structures and devices incorporating such structures are provided. The terms honeycomb or multicellular tubular grid structure as used herein are intended to indicate the network of cellular walls and associated shell portions of the structure when in a free-standing disposition or as imbedded in a composite structure with the cellular passages containing other materials.

Accordingly, it is an object of the present invention to provide a method for fabricating honeycomb or other multicellular tubular grid structures.

Another object of the invention is to provide a method for fabricating honeycomb or other multicellular tubular grid structures in which the progressive detonation of a high explosive is employed to form and/ or fuse assembled components into an integral unit.

Still another object of the present invention is to provide a method for fabricating honeycomb or other multicellular grid structures in which high explosive is disposed in encompassing contiguity with respect to assembled components of said structure and is ignited to produce a progressively propagating annular detonation front effective to form and/ or fuse the assembled components into an integral unit.

A further object of the invention is to provide a method for fabricating honeycomb or other multicellular tubular grid structures in which high explosive is disposed in encompassing contiguity with respect to assembled components of said structure and is ignited to produce a progressively propagating annular detonation front under appropriate conditions to shape and/ or fuse the assembled components into an integral unit.

A still further object of my invention is to provide honeycomb and other multicellular tubular grid structures shaped and/or fused by the detonation of a high explosive for various and sundry utilitarian purposes.

The invention possesses other objects and advantages which will become apparent by consideration of the following specification and accompanying drawing, of which:

FIGURE 1 is a longitudinal sectional view of an explosive jacketed assembly utilized in fabricataing the multicellular tubular grid structures of the invention;

FIGURE 2 is a view along plane 22 as indicated in FIGURE 1;

FIGURE 3 is a longitudinal sectional View of the assembly illustrated in FIGURE 1 at a time during which the fabricating detonation is in progress; and

FIGURE 4 is a cross-sectional view along the plane 44 as indicated in FIGURE 3.

In operating the process of the invention, there is provided an assembly 10 of components as shown in FIG- URE 1 required to provide the shell and interior cellular wall network of the product honeycomb structure together with the elements required to provide an explosive detonation having the essential characteristics. As the initial operation, there is first provided a plurality of elongated elements 11 arranged in parallel contiguity providing a bundle 12 of such elements disposed within a tubular shell or casing 13. Elongated elements 11, as may be seen by reference to FIGURE 2, comprise a tubular cladding layer 14 encompassing a deformable material core 16. Ordinarily, the cladding layer 14 is a uniform thickness tubular layer 14 with a simple circular configuration, but the inner and outher surfaces of such layer 14 may be circular, polyhedral, ribbed longitudinally, corrugated, or be of varying thickness, etc., insofar as the capabilities of the explosive fabrication procedure is concerned, with attendant wide choice of the product structures which may be produced. The simple circular configuration will satisfactorily produce simple polyhedral honeycomb structures usually of a hexagonal pattern and with a generally uniform Wall thickness when similar diameter cladding layers are used. Correspondingly, more complex honeycomb patterns and variable wall thicknesses are produced with cladding layers of more complex configurations. Also, the character of the interfacial bonding region may vary, e.g., as in porosity, etc.

Two general procedures and combinations thereof may be employed to provide elongated elements 11. In the first, the cladding layer 14 is applied by conventional methods, such as electroplating, dip-coating, vapor plating, extrusion, etc., over a wire or elongated rod form having a surface configuration appropriate to provide the interior cladding surface configuration discussed above. Methods such as plating have proven suitable, for example, for applying thin cladding layers of copper over aluminum or zinc which yielded final cellular wall thicknesses as than as 2 mils of copper with no particular indication that this was as thin as would be ultimately possible. Due to the extreme thinness of such walls, a very open honeycomb structure is produced since the total crosssectional area of the walls may be but a very small fraction of the total area within the tubular shell of the grid structure. The structure which results has a very high strength to weight ratio. Extrusion and other coating methods can also be used to apply thicker coatings, which procedures may often be more rapid and economical.

In accordance with the second general method, the cladding 14 may constitute tubing produced by conventional methods and the core 16 may be of a deformable material of either a permanent or of a fugitive material and which may be disposed within the cladding by any of a number of well known methods. For example, the core material may be melted and flowed into the tubular passage, an elongated solid form may be inserted, powder and pellet forms may be poured and tamped therein or the core and tubing cladding could be co-extruded to provide such clad elements 11. It is also posible to apply a second cladding coat over the tubing or cladding as applied above, if it is desired, for example, to provide a more effective bonding layer, produce interfacial alloys, etc. To provide a bundle assembly as above, it is also possible to utilize corrugated sheeting in which the corrugations are conic sections or are planar polyhedral and which may be matched as in conventional practice to provide an assembly suitable for fabrication and bonding by the present method. This procedure is in effect a modification of the second procedure discussed above.

The sizes of cores and channels encompassing such cores can be varied over wide ranges. Core sizes down to as small as inch, i.e., about .030 inch, have been made using available tubing sizes as cladding with no indication that this is the smallest feasible size. Operations utilizing tubing dimension below about one inch and particularly below /2 inch with wall thicknesses of a few percent to about 30% of the outside diameter of the tubing are suitable for forming and bonding. Likewise, the outer shell thickness can be varied over wide ranges from a few thousandths of an inch to A, /2, or more dependent upon the total diameter of the final fabrication.

The diameter of the bundle 12 of elements 11 can likewise be varied over wide limits. Operations in which the diameter of the tube bundle varied over the range of about A inch to 2% inches gave no indication that these approached minimum and maximum feasible limits, respectively.

Due to the extreme effectiveness of the explosive shaping and bonding operation utilized in the process, it is contemplated that almost any metallic material, as well as other materials of construction such as cermets and the like, may be utilized for such shell and cladding in the absence of any overriding consideration, such as incompatibility from corrosive or physical property degradation or the like. Any of the usual construction metals and metal alloys, as well as the more exotic metals and metal alloys, may be so employed. An exemplary tabulation would include metals and alloys of iron, steel, copper, aluminum, nickel, chromium, titanium, zirconium, tantalum, niobium, uranium, thorium, beryllium, bismuth, cadmium, cerium, silicon, cobalt, gold, silver, platinum metals, magnesium, molybdenum, tungsten, rare earth metals, tin, zinc, and even transuranium metals, such as plutonium. Intermetallic compounds might also be employed, particularly if dispersed in a metallic binder matrix and it may be found desirable to include materials such as metallic oxides, nitrides, carbides, and hydrides, as well as more complex compounds, for specialized applications.

Not only may the above-enumerated individual metals and alloys be joined explosively to themselves, but very effective bonds are obtained between dissimilar metals and alloys and, in some cases, the joined interfaces become alloyed providing advantages not usually associated with a bond obtained between similar materials. In some cases, very unusual alloys can be formed. As examples of bonding, copper may be very easily joined to copper, gold, silver, and steel, as well as many other metals. Steel may be joined to steel, nickel, molybdenum, niobium, and tantalum. Tungsten, zirconium, and aluminum can be joined to steel with more careful adjustment of the explosive conditions. Aluminum can be joined to copper, but a very brittle alloy is formed in the interface region and the weldment is weak. Accordingly, it may be concluded that a few surfaces may be joined with a bond that is not satisfactory for all purposes. As a corollary, a thin layer or cladding of a standard alloying material can be included between the surfaces to be joined in order that a bonding layer of alloy may be formed at the bonding layer interface. It will be appreciated that subsequent heat treatment or resistance heating as by the application of electrical currents or by induction may be used to modify the physical properties of the components, as well as to complete the bonding operation if desired or to modify the overall metallurgical properties of the completed assembly. The cladding layer should be reasonably clean and be free from gross irregularities to provide the most compact and intimate bonds. However, porosity in the interfacial bond area may be desired for some purposes and surfaces with irregularities can be employed to provide such a bond.

In the event it is desired to provide a self-supporting honeycomb structure wtihin a shell or casing in a product in which the cellular passages are to be open, the deformable material core 16 comprises a deformable material which can be easily removed by chemical etching, melting or other similar procedure after the explosive fabrication and bonding operation. For this purpose the core 16 may be considered to be formed of a fugitive material. Materials such as wax, parafiin, low-melting metal or metal alloy of the like which may be melted at a temperature below the cladding or casing melting point may be so utilized. The core material may also be a metal such as zinc, magnesium, aluminum, iron, and the like which may be dissolved by applying simple acid or alkaline agents, such as HCl, H carboxylic acids, NaOH, KOH, and other aqueous, solutions which selectively etch or dissolve the core, but not the cladding or shell materials. Water soluble and materials soluble in other solvents might also be utilized. Also, it is conceivable that tubing could be filled wtih fluids or liquids and sealed and the ends removed subsequent to explosive forming and the fluid or liquids removed by means of suction, by evaporation, etc.

However, for other purposes the aforesaid core may comprise a material which is to remain permanently disposed in the cellular passages providing a composite structure in which the honeycomb matrix may serve to provide strength, rigidity, and other desired physical properties, such as providing thermal conductivity, confer impermeability, control rates of diffusion throughout the composite structure, etc. The core material may likewise comprise a wide variety of metallic, inorganic, intermet-allic materials and the like. For example, the core might comprise a deformable composite cast wire or rod, or a compacted or extruded mixture of metals or other bonding agent with abrasive materials, such as metallic carbides, alundum, sapphire, diamond bort, diamond powder, etc. The shell and cladding in which the core is disposed may then be a material such as nickel, stainless steel, cobalt alloys, and the like which would confer strength and rigidity required, e.g., in drill and tool bits, used, e.g., in drilling and machining operations. Similar composite structures are produced if particulate abrasives are disposed in the tubular passages in which case the explosive forming and bonding causes cladding or tubular material to provide a firm bond.

The method is also suitable for fabricating fuel and control rod elements having a composite structure for nuclear reactors. For example, the core within the tubular passages may comprise metallic fissionable material reactor fuels and fertile materials used in breeder reactors, as well as carbides, silicides, nitrides, oxides, and hydrides of fissionable and fertile materials, control rod and selective neutron poison materials with or without metallic or cermet binder, etc. The cladding and casing of such fuel elements may be a conventional metallic cladding material, such as zirconium, stainless steel, aluminum, titanium, nickel alloy, or the like having suitable neutron economy properties and other properties suitable for use in the nuclear reactor environment. Moderators such as beryllium, graphite, carbon, metal hydrides, or the like may also be included in the core material. With respect to moderators, the cladding and casing may comprise a material, such as beryllium, which would then provide moderation of neutrons in the fuel element, provide thermal conductivity from the interior, serve as a fission product diffusion barrier, and other functions known in the nuclear reactor art. The casing may be a material different from that of the cladding on the foregoing elements as dictated by the requirements of the reactor environment.

The assembly provided in accordance with the foregoing is arranged in a suitable explosive fabrication assembly essentially as shown in FIGURE 1 of the drawing. In the form illustrated therein, the casing 1 3 and elongated elements 11 are of the same coextensive length and the individual elements 11 have a similar diameter; however, the elements 11 may be either longer or shorter than the casing if desired for certain purposes. Moreover, within reasonable limits, the elements 11 need not be of a similar diameter and various patterns of element distributions suitable for special purposes may be utilized. 'For example, elements of smaller diameter might be clustered about a single larger diameter element and a plurality of such clusters arrayed within said casing 13. Moreover, as indicated above, the bundle 12 may have a twisted configuration with the elements then being spirally disposed with respect to the axis of the bundle or the aforesaid clusters may be similarly shaped and arranged. Also, alternate elements may be made longer at one or both ends than adjacent elements in order to facilitate fabrication of desired structures, such as heat exchangers, etc., as described more fully hereinafter.

In accordance with a preferred method of explosively forming and joining the components, assembly 10 is provided with an encompassing or layer jacket 17 of a suitable explosive which extends beyond one end 18 of the assembly 10, providing a projecting jacket portion 19. At the outer end of the jacket portion 18, a planar end cap plate 21 of the high explosive is afiixed providing a cavity region 22 defined by plate 21, jacket portion 19, and end 18 of assembly 10. A gas seal 23 in the form of a thin metal sleeve 23 is disposed to fit closely within projecting explosive jacket portion 19 lining the cavity 22 with the lipportion 24 overlapping end 18 of assembly 10 to exclude gases generated in the explosion from entering interstitial spaces therein. Such gases would usually interfere with bonding and shaping. An inert material of low shock wave transmissivity, such as foamed polystyrene or the like, and formed as a plug 26, is disposed to fill the cavity 22 to minimize the effects of the detonation originating from the end and projecting portions 21 and 19 of the explosive jacket. An electrical explosive detonator is positioned as by means of a-plastic washer 28 at the center of end cap plate 21 of the explosive with attached actuating current conductors 29 leading to a suit-able electrical current generator (not shown). While a uniform jacket thickness of explosive may be used, in some instances, an additional thickness such as the supplementary jacket 30 extending along the mid-section of jacket 17 is of considerable assistance in obtaining more uniform fabrication and bonding.

A wide variety of explosives which can be cast or molded or otherwise fabricated into a uniform thickness jacket can be employed. The jacket need not necessarily be of a close fitting cylindrical form since satisfactory results have also been achieved merely by cutting strips of explosive material and taping same to provide an encompassing enclosure of generally square cross section about such an assembly 10. An end cap with centrally located detonator was attached in the same manner and with the gas seal and inert barrier in place as above. A preferred explosive material for the present purpose is the sheet explosive distributed by du Pout de Numours and Company under the designation Du Pont EL-506D and which comprises PETN and a plastic bonding medium. (PETN is pentaerythritol tetranitrate.) Plastic high explosive mixtures, TNT, HMX, Comp. A, Comp. B, and other similar high explosives may also be used with suitable adjustment of the amount and distribution for differences in explosive power and also as sealed for diflferent sizes of the components being fabricated, as well as for the differences in forming properties of such materials. In theory, the amounts needed can be calculated; however, calculation methods may become costly and uneconomic. The amounts of explosive required may be more easily determined by experimental methods. Enough of the explosive, uniformly distributed along the length of the assembly, is needed to produce deformation of the degree necessary to provide the desired final shape and at least an acceptable degree of bonding between contiguous surfaces, as well as compacting core materials if desired. The use of excessive amounts of explosive is evidenced by the production of voids and other evidence of disassembly produced by the resulting excessively energetic rarefaction wave. Jacket thicknesses .of about 0.075 inch of Du Pont 506D, about a one inch diameter assembly of copper clad aluminum wire, and A3" thick shell provided satisfactory operation.

It is generally preferred that the jacket of high explosive be structurally proportioned and dimensioned and the means utilized to initiate the detonation be of such a character that the ensuing detonation proceeds as an annular ring advancing substantially in a transverse plane along the length of said assembly. For this purpose the single point terminally initiated detonation produced by the arrangement of FIGURE 1 is perhaps the simplest of achievement. However, other similar detonation patterns may be provided as by disposing a plurality of detonators in a girdling position with respect to an end or at a position located inwardly from the ends, e.g., in the mid-portion. Primacord initiation may also serve for these purposes. If the multi-point initiation is at the end, the detonation wave is about as above; however, at inwardly disposed locations the detonation proceeds simul taneously outwards in two opposite advancing annular fronts. The explosive jacket may encompass any selected portion of the length of the assembly in the area in which forming and joining is desired. For forming honeycomb structures intended for use as heat exchangers, only the mid-portion would be jacketed with explosive whereby the free ends of alternate tubes could be gathered and provided with coupling fittings for circulating fluids and/ or gases between which heat exchange is desired. Foamed polystyrene, etc. can be used to protect the projecting ends. Header plates and caps providing plenum spaces might likewise be attached by welding, brazing, etc., for similar purposes. Explosive joining might likewise be employed.

The jacketed assembly may be detonated in air or selected atmospheres with some degree of success. However, since excessive amounts of air or other gases usually interfere with proper bonding, it is preferred that the explosive forming and bonding operation be conducted at reduced pressure somewhat below atmospheric. High vacuum conditions are not necessary and reduced pressures of a few mm. Hg to below about 1 mm. Hg are usually satisfactory. It is advantageous to conduct the operation in a heavy-walled vacuum vessel having a relatively large volume to contain fragments which may be propelled from the assembly and to eliminate the loud detonation noises and severe shock waves produced in air. Utilizing such a device, operations may be conducted Without undue disturbance to workers and adjacent personnel.

The jacketed assembly of FIGURE 1 may be supported at the end opposite the detonator upon a cup shaped block (not shown) with the detonator projecting upwardly within such a vessel. Upon detonation fabrication and bonding occur as shown in FIGURE 3 wherein an advancing annular detonation front 31 is shown at midlength along assembly 10. Gases 32 escaping from the detonation front 31 diverage outwardly while heavy compressional shock waves 33 travel convergently inwards through assembly 10. Following passage of the detonation front 31, the portion 34 of the assembly along which the front 31 and associated shock waves 33 have passed are left in a highly compressed and somewhat constricted condition. Moreover, the wire or rod elements are deformed from the original circular shape to assure a polyhedral shape as shown in FIGURE 4. Contiguous surfaces are joined almost instantaneously to yield an integral bond of utmost tenacity. The interface region is found upon metallographic and crystallographic study to exhibit intermixing to some depth and implied intermixing velocities approach free travel detonation velocities. Therefore, while the bonds have the appearance of thoroughly fused materials, in many cases rather unusual effects are exhibited.

Following fabrication and bonding as produced by the explosive detonation, other appropriate shaping and finishing operations are then employed to produce the final product. For example, the assembly may be sawed transversely into slices and the fugitive material removed by appropriate treatment whereupon a polycellular gridwork remains within the shell portion and the thin disc then might be used as for microwave filters, gas and fluid diffusers, flow collimators, etc. Copper plated over aluminum wire and an etching treatment using HCl was used in this manner to provide microwave wave guide filters. The manner of staggering element ends to provide heat exchanger cores, etc. has been described above. If the element core material is to remain permanently therein, sealing caps may be affixed to cover the ends of the assembly if needed. Also, a completely sealed assembly could be produced by explosive fabrication as by sealing or crimping element ends to close the individual elements and positioning metallic cap plates over the ends of assembly prior to explosive fabrication. In this connection, conically tapered end caps might provide more effective closure. In such an application the shock reducing medium at the end would be reduced in thickness or amount or eliminated and similar explosive configurations Would be used at both ends.

As to the explosives indicated by abbreviations or tradenames in the foregoing: Du Pont EL506D is a mixture of 75% pentaerythritol with 25% butyl rubber; TNT is trinitrotoluene; HMX is cyclotetramethylene tetranitramine; Comp. A is 91% RDX (cyclotrirnethylene trinitramine) with 9% beeswax; and Comp. B is 60% RDX with 40% TNT. Comp. D, a typical plastic explosive, is 90% RDX with 10% of a polyisobutylene-mineral oil binder.

While there has been disclosed in the foregoing what may be considered to be preferred embodiments of the invention, modifications may be made therein within the skill of the art and it is intended to cover all such as come within the scope of the appended claims.

What is claimed is:

1. In a method for fabricating a polyhedral polycellular tubular grid structure, the steps comprising arranging a plurality of elongated slender rod elements comprising a deformable substantially incompressible material core and a metallic cladding disposed thereon in parallel contiguity providing a bundle of such clad elements, said cladding having an exterior configuration providing longitudinal linear areas of contact between adjacent elements and with interstitial spaces therebetween, enclosing at least circumferential portions of said bundle with a casing to prevent gas entry from radial directions into said interstitial spaces, disposing a layer of high explosive substantially in concentric relation about said bundle of elements, and detonating said high explosive to produce an annular detonation front which progresses along said bundle of elements to produce a shock wave converging progressively from opposing sides within said bundle, whereby said elements are deformed to force cladding material into said interstitial spaces and contiguous surfaces of said cladding are bonded along an intermixed interface zone to provide the cellular walls of said grid structure.

2. In a method for fabricating a polyhedral polycellular tubular grid structure, the steps comprising arranging a plurality of elongated slender rod elements having a deformable substantially incompressible material core with a circumferentlally continuous metallic cladding disposed thereover in generally parallel contiguity as a bundle fitting closely within a deformable metallic tubular shell, said cladding have an exterior configuration providing longitudinal linear areas of contact between adjacent elements and with interstitial spaces therebetween, disposing a jacket layer of high explosive to encompass at least a portion of said tubular shell, and igniting said jacket of high explosive to produce an annular detonation front to generate a compressive shock wave converging progressively longitudinally from opposing sides within said bundle effective to deform said elements and force cladding material into said interstitial spaces and bond contiguous cladding surfaces along an intermixed interface zone to yield the cellular walls of said grid structure.

3. The method as defined in claim 2 wherein said cladding of said elongated elements includes an inner metallic layer. not readily bondable to itself and disposed about said deformable core and an outer layer disposed in contact with said inner layer, said outer layer being of metallic material capable of bonding said inner metallic layer of one element to that of an adjacent element.

4. In a method for fabricating a polyhedral polycellular tubular grid structure, the steps comprising arranging a plurality of slender elongated rod elements having a core of deformable removable substantially incompressible material with a metallic cladding of generally circular exterior configuration disposed thereover, said elements being disposed compactly in generally parallel contiguity with interstitial spaces therebetween as a bundle fitting closely within a tubular metallic shell, disposing a jacket layer of high explosive to encompass at least a portion of the length of said shell and bundle of elongated elements, igniting said jacket of high explosive to produce an annular detonation front which progresses along at least a portion of the length of said bundle to generate a compressive shock wave converging progressively in a longitudinal linear region within said bundle effective to deform said elements and to propel said cladding material into interstitial spaces and bond contiguous cladding surfaces along an intermixed interface Zone, and removing said fugitive material core yielding said polyhedral polycellular tubular grid structure.

5. The method as defined in claim 4 wherein said removable core material comprises a soluble material, and wherein said material is removed utilizing a solvent for such soluble material.

6. The method as defined in claim 4 wherein said removable core material comprises a material having a melting point below that of said cladding, and wherein said material is removed by heating said assembly above 7. In a method for fabricating a polyhedral polycellular tubular grid structure, the steps comprising arranging a plurality of slender elongated rod elements having a deformable substantially incompressible material core with a metallic cladding of generally circular exterior configuration disposed thereover, said elements being disposed compactly in generally parallel contiguity with interstitial spaces therebetween to form an assembly of said elements fitting closely within a metallic shell, disposing a jacket layer of high explosive about said shell to encompass at least a portion of the length of said assembly, removing gas from at least the interstices of said assembly to produce a sub-atmospheric pressure therein, and igniting said explosive layer to produce an annular detonation front which progresses along at least a portion of said assembly while excluding entry of gaseous explosion products into said interstitial spaces to generate a convergent compressive shock wave within said assembly effective to deform said cladding into said interstitial spaces and bond contiguous shell and cladding surfaces along an intermixed interface zone to yield the cellular walls of said tubular grid structure.

8. In a method for fabricating a polyhedral polycellular tubular grid structure, the steps comprising disposing a plurality of elongated slender generally circular crosssection rod elements comprising a deformable substantially incompressible material core with a tubular metallic cladding disposed thereover fitting closely within a generally tubular metallic shell in compact contiguity with interstices therebetween as an assembly, disposing a tubular jacket layer of high explosive along at least a portion of the length of said assembly and with a portion extending beyond one end thereof, disposing low shock transmissivity material and gas seal means within said extended explosive layer portion, then disposing the assembly in a region of reduced gas pressure to provide a sub-atmospheric gas pressure within the interstices of said assembly, and igniting said extended explosive layer portion to produce an annular detonation front which progresses along said assembly thereby producing a convergent compressive shock wave within said bundle of elements effective to deform said element cores and cladding to enter said interstices and bond contiguous shell and cladding surfaces along an intermixed interface zone to form the cellular walls of said grid structure.

9. The method as defined in claim 8 wherein said extended explosive jacket layer portion is provided with an end cap plate of high explosive, and detonating cap plate means is affixed to said cap plate and said explosive layer is ignited by said detonating cap means and end cap plate ignited to produce said annular detonation front.

10. The method as defined in claim 8 wherein said cladding and tubular shell is formed of a material selected from the group consisting of nickel, stainless steel, and cobalt alloy and said deformable material core is a granular abrasive material selected from the group consisting of metallic carbide, alundum, sapphire, diamond bort and diamond powder which is to remain in the tubular passages of said grid structure.

11. The method as defined in claim 8 wherein said deformable material core is a material soluble in a selected solvent, said cladding and shell comprise a metallic material insoluble in said solvent, and said method includes the step of contacting said core material with said solvent to selectively dissolve same away from said shell and cladding subsequent to said explosive shock wave deformation and bonding operation.

12. The method as defined in claim 8 wherein said elongated elements are disposed in a spiral configuration in said bundle disposed within said shell.

13. A polycellular tubular grid structure comprising an outer annular metallic shell member, and a polyhedral honeycomb grid having tubular passages extending longitudinally within said shell, said grid comprising at least two metallic layers bonded integrally and homogeneously 10 in an interface region, said interface region comprising an explosively intermixed and fused zone of material derived from said metallic layers to form the walls defining said passages.

14. A polyhedral multicellular structure comprising an outer annular metallic shell member, and a honeycomb grid disposed in said annular shell member providing a plurality of tubular passages extending longitudinally therein, said grid being formed of interconnected metallic polyhedral walls defining said tubular passages, said metal lic polyhedral walls which define said passages being bonded to contiguous polyhedral grid walls and the interior walls of said shell member by an interface zone of explosively intermixed and fused polyhedral wall and shell member metallic material to form an integral polyhedral multicellular structure.

15. A polyhedral multicellular structure as defined in claim 14 wherein said shell member and polyhedral walls comprise copper contiguous to a material selected from the group consisting of copper, gold, silver and steel and said interface zone includes an intermixture of copper and said material.

16. A polyhedral multicellular structure as defined in claim 14 wherein said shell member and said polyhedral walls comprise steel contiguous to a material selected from the group consisting of steel, nickel, molybdenum, tantulum, niobium, tungsten, zirconium, and aluminum and said interface zone includes an intermixture of steel and of said material.

17. A polyhedral multicellular structure as defined in claim 14 wherein said shell and cladding comprises a material selected from the group consisting of nickel, stainless steel and cobalt alloys and a granular abrasive material selected from the group consisting of metallic carbides, alundum, sapphire, diamond bort and diamond powder is disposed in said tubular passages.

18. The method as defined in claim 8 wherein surfaces of said cladding and shell comprise copper contiguous to a material selected from the group consisting of copper, gold, silver and steel.

19. The method as defined in claim 8 wherein surfaces of said cladding and shell comprise steel contiguous to a material selected from the group consisting of steel, nickel, molybdenum, tantulum, niobium, tungsten, zirconium and aluminum.

20. The process as defined in claim 11 wherein said core material is selected from the group consisting of zinc, magnesium, aluminum and iron and said solvent is a reactive aqueous reagent of nonneutral pH.

21. The process as defined in claim 8 wherein said core material is aluminum, and said cladding and tube material is copper, wherein said formed grid structure is sliced transversely, subsequent to bonding and forming and said aluminum core is removed therefrom by dissolution in HCl solution.

22. In a method for fabricating a polycellular polyhedral tubular grid structure, the steps comprising,

(1) producing an assembly including a plurality of generally circular slender elongated rod elements comprising a metallic cladding layer disposed upon a removable deformable substantially incompressible material core, said elements being disposed in parallel contiguity as a bundle in a metallic tubular shell with interstices therebetween, said bundle substantially filling said shell, said cladding and tubular shell being comprised of a material selected from the group consisting of iron, steel, copper, aluminum, nickel, chromium, titanium, zirconium, tantalum, niobium, uranium, thorium, beryllium, bismuth, cadmium, cerium, silicon, cobalt, gold, silver, platinum metals, magnesium, molybdenum, tungsten, rare earth metals, tin, zinc, transuranium metals and alloys thereof,

(2) disposing a tubular layer of high explosive about said shell of said assembly, said layer of explosive having a portion extending beyond one end of said assembly,

(3) disposing low shock transmissive material and gas seal means in said extending portion of said explosive layer,

(4) attaching a detonator assembly to said explosive layer at a location appropriate for initiation of an annular detonation front therein,

(5) then removing gas from at least the interstices of said assembly,

(6) actuating said detonation assembly to ignite said explosive layer to produce an annular detonation front progressing along said assembly thereby producing a progressively convergent compressive shock UNITED References Cited by the Examiner STATES PATENTS French et al 29-480 Everett 29180 Philipchuk et a1 29-504 Pflurnn et a1 29183.5

DAVID L. RECK, Primary Examiner.

Wave in said assembly elfective to simultaneously 15 HYLAND BIZOT, Examiner. 

13. A POLYCELLULAR TUBULAR GRID STRUCTURE COMPRISING AN OUTER ANNULAR METALLIC SHELL MEMBER, AND APOLYHEDRAL HONEYCOMB GRID HAVING TUBULAR PASSAGES EXTENDING LONGTUDINALLY WITHIN SAID SHELL, SAID GRID COMPRISING AT LEAST TWO METALLIC LAYERS BONDED INTERGRALLY AND HOMOGENEOUSLY IN AN INTERFACE REGION, SAID INTERFACE REGION COMPRISING AN EXPLOSIVELY INTERMIXED AND FUSED ZONE OF MATERIAL DERIVED FROM SAID METALLIC LAYERS TO FORM THE WALLS DEFINING SAID PASSAGES. 